Scientists Finally Discover Exactly Why Poison Ivy Makes You Itchy

Scientists working at Harvard University have only just now identified the process that causes your skin to develop a painful, itchy rash after touching poison ivy. Their results were published last month in the journal Nature Immunology.

Poison ivy, as well as related plants like poison oak and poison sumac, produce oils on the surface of their leaves. This oil, called urushiol, undergoes a chemical chain reaction when it contacts your skin, but until now researchers didn't know exactly what that chain reaction involved.

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The reason it took so long for scientists to figure this out is that the process involves a molecule called CD1a. CD1a features prominently in the chain reaction in humans, but the researchers were only studying the reaction in mice, which do not have that molecule.

To get around this hurdle, collaborators from Kyoto University genetically engineered mice to produce the CD1a molecule. When the researchers studied the effects of urushiol on these mice, they found a new antibody that appears to reduce the poison ivy rash.

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As part of the chemical chain reaction caused by urushiol, immune cells in the body release two proteins, interleukin 17 and interleukin 22. These proteins—part of the body's defense mechanism—cause the rash and itchiness associated with poison ivy. The antibody the researchers discovered prevents the immune cells from ever releasing those proteins.

This antibody has the potential to be used as a treatment for exposure to poison ivy or similar plants. It could also be used as a treatment for psoriasis, because those two proteins are also present in people with that condition. The researchers believe that the chemical chain reaction that causes the poison ivy rash could have a lot in common with the chemical reactions that cause psoriasis.

The researchers hope to study the problem further, and possibly release a commercial poison ivy treatment in the near future.